The present invention relates to a capillary bore gas discharge lamp of the general type disclosed in my U. S. Pat. No. 5,055,979 entitled "Gas Discharge Light Source", and in U. S. Pat. No. 4,877,997 to Fein entitled "High Brightness End Viewed Gas Discharge Lamp". As stated in the latter patent, capillary bore gas discharge lamps using mercury have the brightest (highest) light output when the lamp is operated in a temperature range of 10.degree.-70.degree. C. An optimum temperature for mercury vapor lamps appears to be about 40.degree. C. (105.degree. F.), which corresponds to an ideal vapor density.
When a mercury vapor lamp has very different cross-sectional dimensions, the temperature can be different at the different cross-sections. In order to maintain the mercury vapor at a near ideal density in critical bore areas of the lamp envelope, the present invention proposes the use of electrical heater means and/or heat sink means at preselected locations along the lamp envelope.
Photon (light) output is related, at least in part, to the number of vapor molecules under bombardment by the flowing electrons. In the case of low pressure mercury vapor lamps, an optimum number of vapor molecules is apparently obtained when the vapor in the capillary bores is at a temperature of about 40.degree.-70.degree. C. The present invention contemplates heating means and dissipating means for maintaining the vapor in the lamp capillary bore section at or near an optimum operating temperature, i.e., 40.degree. C. in the case of a low pressure mercury vapor lamp.
Temperature non-uniformity is a problem associated with vapor lamp operation. When the vapor temperature in the lamp is not uniform across the envelope space between the lamp electrodes, the vapor tends to migrate toward the cooler regions, thereby possibly condensing vapor and tending to lower the vapor pressure in the cooler zone, at least momentarily. Conversely, hot spots produce low vapor molecule concentrations, thereby tending to reduce photon production. In an overall sense, the vapor pressure may remain at a given value, but localized cool spots or hot spots can adversely affect the light output. Temperature uniformity or constancy in the capillary bore section of the lamp contributes to optimized vapor lamp operation.
The present invention contemplates a mechanism for achieving desired temperature uniformity within and along the capillary bore vapor space in a vapor (gas discharge) lamp.
An overall aim of the invention is to provide a low temperature vapor lamp having a relatively high light output. This is achieved through the use of heating means and heat dissipating means for maintaining a satisfactory vapor operating temperature and density in the capillary bore section of the lamp.